1. Field of the Invention
This invention relates to a process for formation of a water repellent coating film which is suitable for applying, for example, to the fins of a heat exchanger. The present invention further relates to the resulting coated substrates.
2. Description of the Prior Art
Compositions capable of forming a water repellent coating have previously been proposed which comprise fluorine containing thermosetting resin in which the fluorine atom content is 10% or more by weight and granular compound of 5 microns or less in mean particle size. Such compositions are described in Japanese Patent application Kokai (Laid-Open) No. 93225/1994.
The coatings resulting from the compositions mentioned above possess excellent water repellency due to the high contact angle of water droplets compared to that from fluorine containing polyolefin such as poly(tetrafluoroethylene). However, since it is necessary to add 40-200 parts by weight of the granular compound based on 100 parts by weight of the fluorine containing thermosetting resin composition in order to provide a contact angle of water droplets of 150 degrees or more, the resulting coating is inferior in mechanical strength or adhesion when coated directly to a substrate and cured. When the coating is in the form of a paint, it can often be removed from the substrate by rubbing with fingers or peeling adhesive tape from the surface of the paint film. A coating composition with low adhesion would also not be desirable for application to the fin of a heat exchanger which is apt to suffer constant vibrations.